Update Pytest to the latest version to fix tests on Python 3.10

Our tests are filing on Python 3.10 due to [1] so we update Pytest in
`requirements-dev.txt` to the latest version.

[1] pytest-dev/pytest#8546

Author: marcinsulikowski

requirements-dev.txt

@@ -4,9 +4,9 @@ flake8==3.8.3
 tox==3.19.0
 coverage==5.2.1
 Sphinx==1.5.6
-pytest==6.0.1
+pytest==7.1.3
 pytest-cov==2.10.1
 pytest-html==2.1.1
 ddt==1.4.1
 typing
-asynctest==0.13.0
+asynctest==0.13.0